Question

An elevation of intracellular [Ca²⁺] is common to the mechanism of excitation-contraction coupling in which types of muscle?

1) Skeletal muscle
2) Smooth muscle
3) Both skeletal and smooth muscle
4) Neither skeletal nor smooth muscle

Answer 1

Both skeletal and smooth muscle rely on an elevation of intracellular [Ca²⁺] for excitation-contraction coupling. This process is initiated by an action potential which leads to the release of calcium ions that play a key role in muscle contraction.

Step-by-step explanation:

An elevation of intracellular [Ca²⁺] is common to the mechanism of excitation-contraction coupling in both skeletal and smooth muscle. In skeletal muscle, excitation-contraction coupling begins when a muscle fiber's membrane is stimulated to fire an action potential, leading to the release of Ca²⁺ ions from the sarcoplasmic reticulum (SR). These ions then interact with the shielding proteins, allowing myosin to bind to actin and initiate contraction. Likewise, in smooth muscle, the influx of Ca²⁺ ions from both extracellular sources and the limited stores of SR is crucial for triggering contraction. Although the processes differ slightly, the commonality lies in the role of calcium ions in mediating muscle contraction.